It is a long time since consumer devices for digitally recording moving images were commonly used. Nowadays, major data recording media for recording such moving images are shifting from tapes to disks. Since (data of) moving images are randomly accessible by the use of data recording media in the form of disks, images at positions far away on the time axis for playback of the moving images can be quickly played back. More specifically, so-called a playback start point can be located quickly and so-called nondestructively edited contents can now be produced more easily by picking up and merging desired portions of a moving image.
To locate a playback start point or an edit point of a recorded moving image, the moving image needs to be played back. This means that if the moving image is encoded, the moving image needs to be decoded before it can be displayed.
However, when a moving image encoded as a program stream of the MPEG (Moving Pictures Experts Group) 2 technique is to be decoded, a portion to be decoded needs to be located and extracted from the data stream before it can be decoded since the moving image is encoded in units of GOP (Group of Pictures). Control required for this purpose is complicated and computationally time-consuming.
As described above, it is difficult to quickly perform the image at a desired point of an encoded moving image.
On the other hand, various recording techniques for recording encoded moving images on a data recording medium are proposed.
FIG. 1 is a diagram depicting a recording technique for recording a moving image in a contiguous area of a data recording medium at predetermined time intervals for playing back the moving image.
A stream unit 11-1 to a stream unit 11-6 are data produced by dividing the moving image at predetermined time intervals for playing back the moving image. Each of the stream unit 11-1 to the stream unit 11-6 is recorded in a contiguous area of the data recording medium.
When the moving image recorded by the recording technique shown in FIG. 1 is to be read out from the data recording medium, the stream unit 11-1 to the stream unit 11-6 are read out sequentially. When one of the stream unit 11-1 to the stream unit 11-6 is read out first and then another of the stream unit 11-1 to the stream unit 11-6 is to be read out, a seek time or a rotational latency is required between the two stream units.
FIG. 2 is a flowchart illustrating known processing for locating and displaying an edit point. In step S11, a management information file storing management information indicating recording positions of the moving image on the data recording medium is read out. In step S12, stream data in the first frame is read out from the data recording medium in the form of a disk based on the read out management information file.
In step S13, the read-out stream data is stored in a buffer. In step S14, the encoded stream data is decompressed (decoded). In step S15, moving image data and audio data obtained by decompressing the stream data are stored in the buffer downstream. In step S16, the moving image data and audio data are sequentially read out from the buffer downstream to display a moving image based on the moving image data and output audio based on the audio data.
In step S17, it is determined whether a user has issued an instruction for shifting to the subsequent point. If it is determined in step S17 that the user has not issued an instruction for shifting to the subsequent point, displaying the moving image and outputting the audio are continued and the flow returns to step S17 to repeat the determination processing.
If it is determined in step S17 that the user has issued an instruction for shifting to the subsequent point, the flow proceeds to step S18, where stream data in the frame at the specified point is read out from the data recording medium in the form of a disk based on the read-out management information file.
In step S19, the read-out stream data is stored in the buffer. In step S20, the encoded stream data is decompressed (decoded). In step S21, moving image data and audio data obtained by decompressing the stream data are stored in the buffer downstream. In step S22, the moving image data and audio data are sequentially read out from the buffer downstream to display the moving image at the specified point based on the moving image data and output the audio at the specified point based on the audio data.
The procedure returns to step S17, where the processing of reading out stream data in the frame at the specified point from the data recording medium in the form of a disk according to an instruction from the user and decoding the stream data to display a moving image and output audio is repeated.
Also, there is another recording method for generating ClipMark composed of marks indicating distinctive images extracted from an input AV stream as management information for managing the AV stream, and furthermore, for generating PlayListMark composed of marks indicating any images specified by a user from among playback sections corresponding to PlayList defining combinations of predetermined sections in the AV stream to record ClipMark and PlayListMark on a recording medium as separate tables (e.g., refer to Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2002-158965